The present invention is an improvement to the molecular sieve ion-exchange process disclosed in the Chinese patent application CN103768951A.
The Chinese patent application CN103768951A specifically disclosed a molecular sieve ion-exchange process, which comprises: mixing a molecular sieve starting material and water to produce a first slurry; filtering the first slurry to produce a second liquid and a second solid (filter cake); mixing the second liquid and the ionic compound to produce an aqueous ion-containing solution; adjusting the aqueous solution with a basic substance to a pH of higher than 8 and then conducting a solid-liquid separation, and subjecting the resulting liquid phase to a bipolar membrane electrodialysis to produce an acid liquid; ion-exchanging at least a part of the second solid (filter cake) and the acid liquid in an ion-exchange vessel; filtering a mixture obtained from the ion-exchange to produce a first liquid (being acidic) and a first solid (filter cake); treating the first solid (filter cake) to produce an ion-exchanged molecular sieve; and adjusting the first liquid with a basic substance to a pH of higher than 8 and then conducting a solid-liquid separation, and subjecting the resulting liquid phase (an aqueous ion-containing solution) to a bipolar membrane electrodialysis to produce an acid liquid for the use in the ion-exchange.
CN103768951A proposed it is necessary to adjust the first liquid to a pH of higher than 8 before the bipolar membrane electrodialysis.